Edward Turner.

Elements of chemistry : including the history of the imponderables and the inorganic chemistry online

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tin, together with small quantities of other metals which are not essential to the
compound. Cannons are cast with an alloy of a similar kind.

The best bell-metal is composed of 80 parts of copper and 20 of tin ; the In-
dian gong, celebrated for the richness of its tones, contains copper and tin in this
proportion. A specimen of English bell-metal was found by Dr. Thomson to
consist of 80 parts of copper, 10*1 of tin, 5*6 of zinc, and 4*3 of lead. Lead and
antimony, though in small quantity, have a remarkable effect in diminishing the
elasticity and sonorousness of the compound. Speculum-metal, with which mir-
rors for telescopes are made, consists of about two parts of copper and one of tin.
The whiteness of the alloy is improved by the addition of a little arsenic.

Copper and zinc unite in several proportions, forming alloys of great import-
ance in the arts. The best brass consists of four parts of copper to one of zinc \
and when the latter is in a greater proportion, compounds are generated which
are called Tombac, flute hgold, and Pinchbeck. The while copper of the Chinese,
which is the same as the German silver of the present day, is composed, accord-
ing to the analysis of Fyfe, of 40'4 parts of copper, 25'4 of zinc, 31-6 of nickel,
and 2*fi of iron.

The art of tinning copper consists in covering that metal with a thin layer of
tin. in order to protect its surface from rusting. For this purpose, pieces of tin
are placed upon a well-polished sheet of cepper, which is heated sufficiently for
fusing the tin. As soon as the tin liquefies, it is rubbed over the whole sheet
of copper, and if the process is skilfully conducted, adheres uniformly to its sur-
f !<(>. The oxidation of the tin, a circumstance which would entirely prevent
the success of the operation, is avoided by employing fragments of resin or



ALLOYS. t 435

muriate of ammonia, and regulating the temperature with great care. The two
metals do not actually combine ; but the adhesion is certainly owing to their
actual affinity. Iron, which has a weaker attraction than copper for tin, is
tinned with more difficulty than that metal.

ALLOYS OF STEEL.

Messrs. Stodart and Faraday have succeeded in making some very important
alloys of steel with other metals. (Phil. Trans, for 1822.) Their experiments
induced them to believe that the celebrated Indian steel, called wootz, \s an alloy
of steel with small quantities of silicon and aluminium ; and they succeeded in
preparing a similar compound, possessed of all the properties of wootz. They
ascertained that silver combines with steel, forming an alloy, which, although it
contains only l-500th of its weight of silver, is superior to wootz or the best
cast steel in hardness. The alloy of steel with 100th part of platinum, though less
hard than that with silver, possesses a greater degree of toughness, and is there-
fore highly valuable when tenacity as well as hardness is required. The alloy
of steel with rhodium even exceeds the two former in hardness. The compound
of steel with palladium, and of steel with iridium and osmium, is likewise ex-
ceedingly hard ; but these alloys cannot be employed extensively, owing to the
rarity of the metals of which they are composed.

ALLOYS OF SILVER.

Silver is capable of uniting with most other metals, and suffers greatly in mal-
leability and ductility by their presence. It may contain a large quantity of
copper without losing its white colour. The standard silver for coinage contains
about l-13th part of copper, which increases its hardness, and thus renders it
more fit for coins and many other purposes.

ALLOYS OF GOLD.

The presence of other metals in gold has a remarkable effect in impairing its
malleability and ductility. The metals which possess this property in the greatest
degree are bismuth, lead, antimony, and arsenic. Thus, when gold is alloyed
with 1-1 920th part of its weight of lead, its malleability is surprisingly dimin-
ished. A very small proportion of copper has an influence over the colour of
gold, communicating to it a red tint, which becomes deeper as the quantity of
copper increases. Pure gold, being too soft for coinage and many purposes in
the arts, is always alloyed either with copper or an alloy of copper and silver,
which increases the hardness of the gold without materially affecting its colour
or tenacity. Gold coins contain about l-12th of copper.

Nearly all the gold found in nature is alloyed more or less with silver. In a
late elaborate investigation into the constituents of the Uralian ores of gold, G.
Rose found one specimen with 0-16 per cent, of silver, and another with 38-38
per cent. ; but most of the specimens contained 8 or 9 per cent, of silver. It has
been maintained that the native alloys of gold and silver are usually in atomic
proportion. This statement, however, has been amply disproved by G. Rose :
these metals appear to beisomorphous, and hence, like other isomorphous bodies,
they crystallize with each other in proportions altogether indefinite. (Pog. An.
xxiii. 161.)



SALTS.



GENERAL REMARKS ON SALTS.



THE preceding pages contain the description either of elementary principles,
or of compounds immediately resulting from the union of those elements. These
compounds are chiefly bi-elementary, that is, arise from the union of two ele-
ments; their constituents are regarded, according to the electro-chemical theory,
possessing opposite, electric energies, and as combined by virtue of such ener-
gies ; and the names applied to them are partly constructed in reference to this
theory, t'hus in compounds of oxygen and chlorine, chlorine and iodine, sul-
phur and potassium, the term expressive of the genus or class of bodies to which
each compound belongs, is derived from the electro-negative element ; so that
we do not say, chloride of oxygen, iodide of chlorine, and potassiuret of sulphur,
but, oxide of chlorine, chloride of iodine, and sulphuret of potassium; because
oxygen has a higher electro-negative energy than chlorine, chlorine than iodine,
and sulphur than potassium. The metals as a class are electro-positive to the
non-metallic elements ; but in relation to each other some of the metals are elec-
tro-positive, and others electro-negative. To the former belong those metals,
the oxides of which are strong alkaline bases, such as potassium, sodium, and
calcium ; and among the latter are enumerated those, such as arsenic, antimony,
and molybdenum, which are prone to form acids when they unite with oxygen.

Some of the bi-elementary compounds above referred to, though composed of
very energetic elements, are themselves chemically indifferent, manifesting little
disposition to unite with any other body whatever; of which the peroxides of
manganese and lead, and some of the chlorides are examples. Others, on the
contrary, are surprisingly energetic in their chemical relations, and have an ex-
tensive range of affinity. The most remarkable instances of this are found among
those oxidized bodies called acids and alkalies, the characters of which fixed the
attention of chemists long before their composition was understood. The acids
and alkalies, however, are indifferent to elementary substances: their affinities
are exerted towards each other, and by upiting they give rise to compounds
more complex than themselves, as containing at least three elements, and which
are known by the name of salts. Acids and alkalies possess opposite electric
energies in relation to each other, the former being and the latter -f-. The
electric energies evinced by them are related to the electric energies of their



GENERAL REMARKS ON SALTS. 437

elements. Thus acids generally abound in the electro-negative oxygen, and if
they contain a metal, it is usually an electro-negative metal ; whereas the pow-
erful alkalies are the protoxides of electro-positive metals. .

Acids and alkalies neutralize each other more or less completely, so that the
resulting salt is generally neither acid nor alkaline, and is far less energetic as
a chemical agent than acids and alkalies. Most of them, however, unite in defi-
nite proportion with certain substances, such as water, alcohol, ammonia, and
with other salts, forming the extensive family of double salts. To these com-
pounds the electro-chemical theory may be extended : the two simple salts which
constitute a double salt, may be viewed as two molecules united by virtue of
electric energies of an opposite character.

In the early period of modern chemistry an acid was considered to be an oxi-
dized body which has a sour taste, reddens litmus paper, and neutralizes alka-
lies. But subsequent experience has shown the propriety of extending the defi-
nition of an acid. For, first, the discovery of the hydracids proved that oxygen
is not essential to acidity. Secpndly, some compounds, owing to their insolu-
bility, neither taste sour nor redden litmus, and yet from their chemical relations
are regarded as acids. Thirdly, some acknowledged acids, such as the carbonic
and hydrosulphuric, are unable fully to destroy the alkaline reaction of potassa.
Facts of this kind have induced chemists to consider as acids all those com-
pounds which unite with potassa or ammonia, and give rise to bodies similar
in their constitution and general character to the salts which the sulphuric or
some admitted acid forms with those alkalies.

A similar extension is given to the notion of alkalinity, tbe characters of which,
as exhibited in their most perfect form in potassa and soda, are causticity, a
peculiar pungent alkaline taste, alkaline reaction with test paper, and power both
of neutralizing acids and of forming with them neutral saline compounds. Of
these, chemists agree to consider the last as the most characteristic, and place
among the alkaline, or salifiable bases all those bodies which unite definitely with
admitted acids, such as the sulphuric and nitric, and form with them compounds
analogous in constitution to the salts which admitted alkalies form with the
acids. Thus, magnesia is a very strong alkaline base, seeing that 20-7 parts of
it neutralize as much sulphuric acid as 47 of potassa; and yet magnesia, from
being insoluble is all but tasteless, and has barely any alkaline reaction.

The progress of chemistry, which has gradually developed sounder views ot
the nature of acids and alkalies, is also causing an extension in the" idea of a
salt. The great mass of the salts are compounds of oxidized bodies, both the
acid and the base containing oxygen. But ammonia, though not an oxide, has
all the characters of alkalinity in an eminent degree, and its compounds with
acids were at once admitted into the list of salts. Then came the discovery of
the hydracids, such as the hydrochloric and hydriodic, which are so powerfully
acid, that their compounds with alkaline bases were readily adopted as salts.
Hence arose the division of the salts as a class into two orders, one containing
the oxygen or oxy-salts, and the other the hydrogen or hydro-salts. Again, the
gaseous terfluoride of boron, which contains neither oxygen nor hydrogen, com-
bines definitely with ammonia, and forms with it a neutral compound, which was
esteemed a salt as soon as it was known.

The notion of a salt has of late been still further extended. Chemists have
long known that metallic sulphurets occasionally combine together, and consti-
tute what is called a double sulphurd. In these compounds Berzelius, whose



438 GENERAL REMARKS ON SALTS.

labours have greatly added to their number, has traced an exact analogy with the
salts, and applied to them the name of sulphur-salts. The simple sulphurets by
the union of which a > sulphur-salt is formed, are bi-elernentary compounds, strictly
analogous in their constitution to acids and alkaline bases, and which, like them,
are capable of assuming opposite electric energies in relation to each other.
Electro-positive sulphurets, termed sulphur bases, are usually the protosulphurets
of electro-positive metals, and therefore correspond to the alkaline bases of those
metals; and the electro-negative sulphurets, sulphur-acids, are the sulphurets of
electro-negative metals, and are proportional in composition to the acids which
the same metals form with oxygen. Hence, if the sulphur of a sulphur-salt were
replaced by an equivalent quantity of oxygen, an oxy-salt would result. (An.
de Ch. et Ph. xxxii. 60.)

The compounds which Berzelius has enumerated as sulphur-acids, are the sul-
phurets of arsenic, antimony, tungsten, molybdenum, tellurium, tin, and gold.
To these he has added the sulphurets of several other substances not metallic,
such as sulphuret of selenium, bisulphuret of carbon, and the hydrosulphuric
and hydrosulphocyanic acids. He mentions, also, that just as two electro-posi-
tive oxides may combine, one becoming electro-negative in regard to the other,
so may a sulphur-salt be generated by the union of electro-positive sulphurets.
The native double sulphuret of copper and iron, and a considerable number of
similar compounds, are instances of this nature. These analogies are rendered
much closer by the facts that hydrosulphuric and hydrosulphocyanic acids act
as hydro-acids with ammonia, and as sulphur-acids with sulphur-bases; and that
all the sulphurets which are remarkable as sulphur-acids, have likewise the pro-
perty of combining with ammonia. I shall accordingly place the double sul-
phurets as a third order of the class of salts, and describe them under the name
of sulphur-salts.

A fourth order of salts has been formed by Berzelius, comprising for the most
part bi-elementary compounds, which consist of a metal on the one hand, and of
chlorine, iodine, bromine, fluorine, and the radicals of the hydracids on the other.
He has applied to them the name of haloid-salts (from axj sea-salt, and eidof
form), because in constitution they are analogous to sea-salt. The whole series
of the metallic chlorides, iodides, bromides, and fluorides, such as chloride of
sodium, iodide of potassium, and fluor-spar, as well as the cyanides, sulpho-
cyanides, and ferrocyanides, are included in the list of haloid-salts. (An. de
Ch. et Ph. xxxii. 60.) The reader will at once perceive that these haloid-salts,
as bi-elementary compounds, differ in composition from other salts, and are analo-
gous to oxides and sulphurets.

The preceding pages contain an account of the different classes of compounds
which have been termed salts. But since the last edition of this work was pub-
lished, new views on this important class of bodies have begun to prevail. The
researches of Graham on the phosphates, those of Liebig on the constitution of
the organic acids and their salts, and the experiments of Dumas, Clark, Fremy,
Thiiulow, Peligot, and many others, have gradually converged to the point of
recalling to the recollection of chemists certain profound views, first suggested
by Davy in regard to chloric and iodic acids and their salts, and afterwards
applied (apparently without previous knowledge of what Davy had done) by
Dulong to the snlts of oxalic acid. These views have thr inestimable advantage
of uniting all acids into one series, and all salts into another; nay, those two
series may even be considered as one. I shall here briefly explain them; but in



GENERAL REMARKS ON SALTS. 439

describing the salts individually, I shall retain the usual views of the constitu-
tion of acids and salts, as the former have been thus described in the preceding
part of this volume, and the chemical world is not yet ripe for a complete change
in the theory of salts. The new views, however, are making such rapid pro-
gress, and are so closely entwined with the details of every part of chemistry,
that a knowledge of them is indispensable to the student.

In regard to acids, then, the first point to be noticed is, that all so-called oxy-
gen acids, in the free, or what may be called the active state, contain hydrogen.
On referring to the description of the mineral acids it will be found, for example,
that they are described as combining with water when separated from their com-
bining actions. Oil of vitriol is SO 3 ,HO ; nitric acid N0 5 ,HO, &c. The latter,
indeed, cannot exist in the supposed anhydrous state, NO 5 ; and this is the case
with a large majority of all known acids. Sulphuric acid and phosphoric acid,
no doubt, may be obtained anhydrous, So 3 and P 2 O 5 ; but it is worthy of especial
notice, that in this state they do not possess the properties of these acids, and only
acquire them on the addition of water. The compound of dry sulphuric acid
and ammonia, SO 3 ,NH 3 , is not sulphate of ammonia, but a distinct compound.
Moreover, these anhydrous acids combine with water with the greatest vehe-
mence, and then assume their active characters. The principal exceptions are
carbonic acid and chromic acid ; but, on the other hand, none of the organic
acids can exist without water, that is, without hydrogen.

It is obvious that hydrogen is essential to the hydracids. Now the view which
I wish here to explain considers both these classes of acids as hydracids, and
thus unites in one class or series bodies having the most perfect analogy in pro-
perties. According to this view, therefore, the general formula of a hydracid is
X -f- H : X being an acid-radical which may be either simple or compound.
Thus in hydrochloric, hydriodic, and hydrosulphuric acids respectively, X is
represented by C1,I, or S. In hydrocyanic and hydrosulphocyanic acids, X is
represented by Cy = C 2 N, and by CyS 2 = C 2 NS 2 , respectively.

In the hydrated oxygen acids of the preceding pages, to which alone, and not
to the anhydrous acids, this theory applies, X is always a compound, and always
contains oxygon. Thus in hydrated sulphuric acid, commonly so called, and
represented by S0 3 ,HO, X is represented by SO 4 : in nitric acid, N0 5 Ht), X =
NO g ; and in metaphosphoric acid, P 2 5 ,HO, X= P 2 O g : and the true formulae
of these acids are SO 4 ,H,N0 6 ,H and P 2 O g ,H, respectively.

Further, among the organic acids to be afterwards described, we find a corres-
ponding constitution. In acetic acid (hydrated) C 4 H S O 3 ,HO, X = C 4 H 3 O 4 ; in
hydrated formic acid, C 2 HO 3 ,HO, X == C 2 H0 4 , &c.

The next point to be noticed is, that acids exist, the general formula of which
is X -f- H n ; that is, in which X combines with two or more equivalents of H,
and which are called polybasic acids. Those acids, above described, in which
there is 1 eq. of H, are called monobasic acids. Where 2 eq. of H are present
the acid is bibasic ; with 3 eq. of H, tribasic, and so on. The reason of this
nomenclature will appear when we come to salts.

Examples of this kind are, pyrophosphoric acid, P 2 O 5 ,2HO, which is bibasic,
its true formula being P 3 O 7 ,H 2 ; phosphoric acid, P 2 O 5 ,3HO, which is a tri-
basic acid, P O ,H ; and arsenic acid, As O 5 ,3HO ; also a tribasic acid,
As 2 8 ,H 3 .

But it is among the organic acids that we find the most numerous and striking



440 GENERAL REMARKS ON SALTS.

examples of polybasic acids. The following table contains the formulae of some
of these.



Meconic acid . . . C M H O n + 3HO (tribasic) = C U H

Cyanuric acid . . . Cy 3 3 -fr 3HO (tribasic) = Cy 3 6 -f H 3 .

Citric acid .... C^H^O,, -j- 3HO (trihusic) = C, 2 H 5 Ou + H 3 .

Tannic acid . . . C 18 H 5 9 -\- 3HO (tribasic) = C I8 H 5 0, 2 -f- H 3 .

Tartaric acid . . . C 8 H 4 0, -j- 2HO (bibasic) =C 8 H 4 0, 2 + H 2 .

Komenic acid . . . C I2 H 2 8 + 2HO (bibasic) = C, 2 H 2 0, -f- H 2 .

Fulminic acid . . . Cy 2 2 + 2HO (bibasic) = Cy 2 O 4 -f- H 2 .

Mucic acid . . . . C| 2 H 8 O U -f- 2HO (bibasic) =C,2H 8 Oi6 + H 2 .

Moreover there are also polybasic acids which contain no oxygen, analogous
in this respect to hydrochloric and hydrocyanic acids. Thus ferrocyanic acid is
represented by Cy 3 Fe -f H 2 ; and ferridcyanic acid is Cy 3 Fe 2 -f- H 3 .

It will be obvious at a glance, that this theory of acids possesses the advan-
tages of simplicity and of uniting in classification a vast number of bodies,
similar in properties, which have formerly been arbitrarily separated. But the
chief advantage attending it is, that it enables us to effect the same union into
one class of all the salts of the acids containing hydrogen. It is in examining
the salts, moreover, that we find the strongest arguments in favour of the theory
as applied to acids.

A salt is formed, whenever one of these acids is neutralized by a metallic
oxide, by ammonia, or by an organic base, or combines with them, without being
neutralized.

Now, when a salt is thus formed, one phenomena constantly occurs ; this is
the separation oif water. In the simplest case, namely, where the hydracid of
an elementary body acts on a metallic protoxide, the origin of the water is quite
obvious. When hydrochloric acid, for example, acts on oxide of silver, chloride
of silver is formed, and water is eliminated : HC1 -f- AgO = AgCl -f- HO.
There is here no doubt that the water is produced by the reaction.

But when hydrated sulphuric acid acts on the same oxide, although the phe-
nomena are exactly the same, a different explanation is commonly given ; and
the water is assumed to have pre-existed in the acid, thus, SO 3 ,HO -f- AgO =
SO 3 ,AgO + HO.

It is contrary to all sound principles of reasoning to adopt two explanations of
facts precisely similar; where one will suffice, and only one explanation of the
former case is possible, we must apply the same explanation to the latter. This
is clone by the new theory ; and the following formulae will show the identity of
the reaction in the two cases :



H,C1 f Ag r O

H,S0 4 + AgO= Ag,S0 4 -|- HO.

In both cases the water is formed by the union of the hydrogen of the acid with
the oxygen of the oxide; and consequently in both cases the hydrogen of the
acid has been replaced by the metal.

Here, then, is the theory of salts. A salt is formed when the hydrogen of the
acid is replaced by its equivalent of a metal. Consequently, acids may be viewed
as the hydrogen salts of their radicals, and thus acids and salts, in regard to
their constitution, will form but one class.



GENERAL REMARKS ON SALTS. 441

As the metals replace hydrogen equivalent for equivalent, it is obvious that
polyhasic acids will form poly basic salts. This has already been illustrated
under phosphoric acid, but other examples may be given. Thus, when cyanuric
acid acts on oxide of silver, 3 atoms of the latter are required for one of the
former, (Cy 3 O 6 t H 3 ) + 3AgO = (Cy 3 O 6 t Ag 3 ) -j- 3HO. With fulminic acid
2 atoms are required, (Cy a O 4 + H a ) + 2AgO = (Cy 2 O 4 + Ag 2 ) + 2HO. It is
unnecessary here to multiply these examples.

One remarkable consequence, deducible from the theory under consideration
is, that those oxides which most easily lose oxygen should most readily replace
by their metal the hydrogen of the acid. This is found to be the case. For
example, potash can only replace by potassium 2 of the 3 eq. of hydrogen in
cyanuric acid, and 1 of the 2 eq. of hydrogen in fulminic acid, forming the

K C K }

compounds, Cy 3 O g 2 < and Cy 2 O 4 _, > while with oxide of silver, an easily

reducible oxide, the replacement as before mentioned, is complete. This fact
furnishes an almost irresistible argument for the existence of hydrogen, as such,
in acids ; and further explains the formerly unaccountable fact, that the salts
formed by the action of oxide of silver on organic acids are always anhydrous.
In the case of phosphoric and arsenic acids also, oxide of silver forms anhy-
drous salts, or, in other words, replaces the hydrogen entirely, with much greater
facility than potash or soda.

Another obvious consequence of this theory is, that the neutralizing power of
an acid depends entirely on the number of equivalents of hydrogen replaceable
by metals. Take, for example, hydrosulphuric acid, S -f- H ; and add to the
radical oxygen, &c., in almost any proportion, the neutralizing power remains
unchanged, as the following table shows :



Hydrosulphuric acid . . . S ~j~H.

Sulphurous acid . . . . S0 3 -f-H.

Sulphuric acid . , . . SO4 -j-H.

Hyposulphurous acid . . . S. 2 3 -|-H.

Hyposulphuric acid . . . S20 6 -}-H.

Hydrosulphocyanic acid . . . S 2 Cy ~}~H.

Chlorosulphuric acid . . . S0 3 Cl-f-H. (Regnault,)

Nitrosulphuric acid . . . SNOs-j-H. (Pelouze.)

No substances can be more different in composition than the above ; yet they
all neutralize exactly the same quantity of base ; a fact readily explained, when



Online LibraryEdward TurnerElements of chemistry : including the history of the imponderables and the inorganic chemistry → online text (page 63 of 119)